The present invention relates generally to power supplies, and more particularly, is directed to a power supply for a portable telephone or other small electronic device.
Conventionally, portable telephones have a power supply consisting of several batteries in series, to provide an unregulated voltage, connected to a voltage regulator. In the case of linear regulation, the voltage produced by the battery cells is greater than that of the regulated output. For most portable phones, this arrangement is accomplished with five batteries in a battery pack, and an external regulator in the telephone. The result is a large, heavy and expensive battery.
Alternatively, a switching power supply can be used to allow an output voltage which is greater than the battery voltage, thereby allowing a reduction in the number of battery cells. A reduction from five cells to even one cell is possible. This approach is rarely used because of radiated and conducted EMI (electro-magnetic interference), and requirements for low-ripple (low noise) on the regulated output.